As a well known fact, surveillance radar performance may be significantly degraded by the presence of clutter echoes, which are characterized by parameters not known a priori and which vary in a random fashon.
To counter the effects of such disturbances, the techniques normally resorted to are the fixed MTI and the adaptive MTI. The acronym MTI, "Moving Target Indicator", is commonly in use by experts in the field and shall be used from here on for convenience.
In the case of fixed MTI (L. E. BRENNAN et Al. IEEE Trans. on AES Vol. AES-9, No. 2 March 1973) the clutter carrier frequency is assumed to be known and a fixed parameter filter is used to cancel it.
In the case of adaptive MTI (U.S. Pat. No. 4,217,584 GALATI LOMBARDI/SELENIA) the clutter carrier frequency is estimated from the signal received by the radar and the filter profile is shifted so as to overlay the disturbance spectrum with its opaque band.
These two techniques give way to the following drawbacks:
fixed parameter filter, therefore predetermined filter profile; PA1 limited performance in the presence of more than one clutter signal; PA1 limited sensitivity of the useful signal; PA1 partly correlated cancellation residue which is therefore integrated in the following processing stages with a resulting higher false alarm probability. PA1 precision of the steady state estimate D, PA1 high speed to adapt to non stationary disturbance conditions.